CN117769659A - RFID tag parameter determination using phase - Google Patents

Abstract

RFID tag reply phase measurements may be used to estimate tag position and motion. The phase measurements may be used to directly calculate tag position/motion or to generate a probability of correlation with candidate tags having different position/motion characteristics. The RFID reader system may make multiple phase measurements for a tag at different carrier frequencies within a single inventory round to ensure that the tag remains within range of the reader system.

Description

RFID tag parameter determination using phase

Background

Radio-frequency identification (RFID) systems typically contain an RFID reader, also known as an RFID reader/writer or RFID interrogator, and an RFID tag. RFID systems can be used in many ways for locating and identifying objects to which tags are attached. RFID systems are useful in the product-related and service-related industries for tracking objects being processed, inventoried, or disposed of. In these cases, the RFID tag is typically attached to the individual item or to its packaging. RFID tags typically contain or are Radio Frequency (RF) Integrated Circuits (ICs).

In principle, RFID technology requires the use of an RFID reader to inventory one or more RFID tags, where inventory involves separating tags, receiving identifiers from tags, and/or acknowledging received identifiers (e.g., by transmitting an acknowledgment command). "singulation" is defined as the possibility that a reader may individually pick a tag out of a plurality of tags for use in a reader-tag conversation. An "identifier" is defined as a number that identifies the tag or the item to which the tag is attached, such as a Tag Identifier (TID), an Electronic Product Code (EPC), and so forth. "inventory round" is defined as the reader ranking RFID tags for continuous inventory. The reader transmitting the RF wave performs inventory. The RF wave is typically an electromagnetic wave at least in the far field. RF waves may also be primarily electric or magnetic waves in the near field or transitional near field. The RF wave may encode one or more commands that instruct the tag to perform one or more actions. The operation of an RFID reader to send commands to an RFID tag is sometimes referred to as a reader "interrogating" the tag.

In a typical RFID system, an RFID reader transmits a modulated RF inventory signal (command), receives a tag reply, and transmits an RF acknowledgement signal in response to the tag reply. Tags that reply to the interrogating RF wave reply by transmitting back another RF wave. The tag generates the transmitted back RF wave either originally or by reflecting back a portion of the interrogating RF wave in a process known as back scattering. Backscattering can occur in a number of ways.

The reflected RF waves may encode data (e.g., numbers) stored in the tag. The response is demodulated and decoded by a reader, which in turn identifies, counts, or otherwise interacts with the associated item. The decoded data may represent a serial number, price, date, time, destination, encrypted message, electronic signature, other attributes, any combination of attributes, and so forth. Thus, the reader may learn about the item with the tag and/or about the tag itself when the reader receives the tag data.

RFID tags typically include an antenna section, a radio section, a power management section, and often include a logic section, memory, or both. In some RFID tags, the power management section includes an energy storage device, such as a battery. RFID tags having energy storage devices are known as battery-assisted semi-active or active tags. Other RFID tags may be powered only by the RF signals they receive. Such RFID tags do not include an energy storage device and are referred to as passive tags. Of course, even passive tags typically contain temporary energy and data/flag storage elements, such as capacitors or inductors.

Disclosure of Invention

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter.

Embodiments are directed to using RFID tags to reply to phase measurements to estimate tag position and motion. The phase measurements may be used to directly calculate tag position/motion or to generate a probability of correlation with candidate tags having different position/motion characteristics. The RFID reader system may make multiple phase measurements for the tag at different carrier frequencies within a single inventory round to ensure that the tag remains within range of the reader system.

These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.

Drawings

The following detailed description is made with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of components of an RFID system.

Fig. 2 is a diagram illustrating components of a passive RFID tag, such as may be used in the system of fig. 1.

Fig. 3 is a conceptual diagram illustrating a half-duplex mode of communication between components of the RFID system of fig. 1.

Fig. 4 is a block diagram showing details of an RFID tag, such as the RFID tag shown in fig. 2.

Fig. 5A and 5B illustrate signal paths during tag-to-reader and reader-to-tag communications in the block diagram of fig. 4.

Fig. 6 is a block diagram illustrating details of an RFID reader system, such as the RFID reader system shown in fig. 1.

Fig. 7 depicts tag parameter determination using phase according to an embodiment.

Fig. 8 depicts components of an RFID reader system according to an embodiment.

Fig. 9 depicts how static reflection may be used to calibrate an RFID reader transceiver according to an embodiment.

FIG. 10 depicts how dynamic reflection may be used to calibrate an RFID reader transceiver according to an embodiment.

FIG. 11 depicts how dynamic reflection in a radiating environment may be used to calibrate an RFID reader system according to an embodiment.

Fig. 12 depicts how RFID tag parameters may be determined by correlation with candidates according to an embodiment.

Fig. 13 depicts a diagram of how correlation may be used to determine RFID tag range according to an embodiment.

Fig. 14 depicts example baseband, modulated, and modulated waveforms at an RFID reader according to an embodiment.

Fig. 15 depicts delimiter symbols according to the Gen2 protocol.

Detailed Description

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments or examples. These embodiments or examples may be combined, other aspects may be utilized, and structural changes may be made without departing from the spirit or scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

As used herein, a "memory" is one of ROM, RAM, SRAM, DRAM, NVM, EEPROM, FLASH, fuse, MRAM, FRAM, and other similar volatile and non-volatile information storage technologies. Some portions of the memory may be writable and some portions may not be writable. An "instruction" means a request to a tag to perform a single explicit action (e.g., write data into memory). "command" means that the reader requests one or more tags to perform one or more actions and includes one or more tag instructions preceded by a command identifier or command code that identifies the command and/or tag instruction. "program" means a request to a tag to execute a set or sequence of instructions (e.g., read a value from memory and lock a memory word if the read value is less than a threshold). "protocol" means industry standards for communication between readers and tags (and vice versa), such as version 1.2.0, 2.0, and 2.0.1 of the type 1, 2 nd generation UHF RFID protocol ("Gen 2 protocol") for communication at 860MHz-960MHz, of the GS1 EPCglobal company, which is hereby incorporated by reference.

Fig. 1 is a diagram of the components of a typical RFID system 100 incorporating an embodiment. The RFID reader 110 and nearby RFID tags 120 communicate via RF signals 112 and 126. When transmitting data to the tag 120, the reader 110 may generate the RF signal 112 by encoding the data, modulating an RF waveform with the encoded data, and transmitting the modulated RF waveform as the RF signal 112. In turn, tag 120 may receive RF signal 112, demodulate encoded data from RF signal 112, and decode the encoded data. Similarly, when data is transmitted to reader 110, tag 120 may generate RF signal 126 by encoding the data, modulating an RF waveform with the encoded data, and causing the modulated RF waveform to be transmitted as RF signal 126. The data transmitted between the reader 110 and the tag 120 may be represented by symbols, also referred to as RFID symbols. The symbols may be delimiters, calibration values, or implemented to represent binary data, such as "0" and "1", as desired. After processing by the reader 110 and the tag 120, the symbol may be considered a value, a number, or any other suitable representation of data.

The RF waveform transmitted by the reader 110 and/or the tag 120 may be in a suitable frequency range, such as near 900MHz, 13.56MHz, or the like. In some embodiments, RF signals 112 and/or 126 may include non-propagating RF signals, such as reactive near-field signals or the like. The RFID tag 120 may be active or battery-assisted (i.e., having its own power source), or passive. In the latter case, the RFID tag 120 may collect power from the RF signal 112.

Fig. 2 is a diagram 200 of an RFID tag 220 that may serve as tag 120 of fig. 1. The label 220 may be formed on a substantially planar inlay 222 that may be fabricated in any suitable manner. Tag 220 contains circuitry that may be implemented as an IC 224. In some embodiments, IC 224 is fabricated in Complementary Metal Oxide Semiconductor (CMOS) technology. In other embodiments, IC 224 may be fabricated in other technologies, such as Bipolar Junction Transistor (BJT) technology, metal-semiconductor field effect transistor (MESFET) technology, and other technologies well known to those skilled in the art. The IC 224 is disposed on the inlay 222.

Tag 220 also includes an antenna for transmitting and/or interacting with RF signals. In some embodiments, the antenna may be: etched, deposited, and/or printed metal on inlay 222; conductive lines formed with or without the substrate 222; non-metallic conductive (e.g., graphene) patterning on substrate 222; a first antenna inductively, capacitively, or galvanically coupled to the second antenna; or may be manufactured in a variety of other ways for forming an antenna to receive RF waves. In some embodiments, the antenna may even be formed in the IC 224. Regardless of the antenna type, the IC 224 is electrically coupled to the antenna via suitable IC contacts (not shown in fig. 2). The term "electrically coupled," as used herein, may mean a direct electrical connection, or it may mean a connection that includes one or more intervening circuit blocks, elements, or devices. The term "electrically" portion of "electrically coupled" as used in this document shall mean coupling of one or more of ohmic/galvanic, capacitive and/or inductive. Similarly, the term "electrically isolated" or "electrically decoupled" as used herein means that one or more types (e.g., galvanic, capacitive, and/or inductive) of electrical coupling are absent, at least to the extent possible. For example, elements that are electrically isolated from each other are galvanically isolated from each other, capacitively isolated from each other, and/or inductively isolated from each other. Of course, an electrically isolated component will typically have some unavoidable stray capacitive or inductive coupling between them, but the purpose of isolation is to minimize this stray coupling when compared to the electrically coupled path.

IC 224 is shown with a single antenna port including two IC contacts electrically coupled to two antenna segments 226 and 228, which are shown here as forming a dipole. Many other embodiments are possible using any number of ports, contacts, antennas and/or antenna segments. Antenna segments 226 and 228 are depicted as being separate from IC 224, but in other embodiments antenna segments may alternatively be formed on IC 224. Tag antennas according to embodiments may be designed in any form and are not limited to dipoles. For example, the tag antenna may be a patch, slot, loop, coil, horn, spiral, monopole, microstrip, stripline or any other suitable antenna.

The drawing 250 depicts top and side views of a label 252 formed using a strip. Tag 252 differs from tag 220 in that it includes a substantially planar strap substrate 254 having strap contacts 256 and 258.IC 224 is mounted on strap substrate 254 such that IC contacts on IC 224 are electrically coupled to strap contacts 256 and 258 via suitable connections (not shown). The strap substrate 254 is then placed over the inlay 222 such that the strap contacts 256 and 258 are electrically coupled to the antenna segments 226 and 228. The strap substrate 254 may be attached to the inlay 222 via a press, an interface layer, one or more adhesives, or any other suitable means.

The drawing 260 depicts a side view of an alternative way of placing the strap substrate 254 onto the inlay 222. The surface of the strap substrate 254 that includes strap contacts 256/258 does not face the surface of the inlay 222, but rather the strap substrate 254 is positioned with its strap contacts 256/258 facing away from the surface of the inlay 222. Strap contacts 256/258 may then be capacitively coupled to antenna segments 226/228 through strap substrate 254 or conductively coupled to antenna segments 226/228 using perforations that may be formed by crimping strap contacts 256/258. In some embodiments, the positions of the strap substrate 254 and inlay 222 may be reversed, with the strap substrate 254 mounted under the inlay 222 and the strap contacts 256/258 electrically coupled to the antenna segments 226/228 through the inlay 222. Of course, in still other embodiments, strap contacts 256/258 may be electrically coupled to antenna segments 226/228 through both inlay 222 and strap substrate 254.

In operation, the antenna couples with RF signals in the environment and propagates the signals to the IC 224, which may collect power and respond as appropriate based on the incoming signals and the internal state of the IC. If IC 224 uses backscatter modulation, it may generate a response signal (e.g., signal 126) from an RF signal in the environment (e.g., signal 112) by modulating the reflectivity of the antenna. The IC contacts of the electrically coupled and decoupled IC 224 may modulate the reflectivity of the antenna, thereby changing the admittance or impedance of the parallel-connected or series-connected circuit elements coupled to the IC contacts. If the IC 224 is capable of transmitting a signal (e.g., has its own power source, is coupled to an external power source, and/or may collect sufficient power to transmit a signal), the IC 224 may respond by transmitting a response signal 126. In the embodiment of fig. 2, antenna segments 226 and 228 are separate from IC 224. In other embodiments, antenna segments may alternatively be formed on IC 224.

RFID tags, such as tag 220, are often attached to or associated with individual items or item packages. The RFID tag may be manufactured and then attached to the article or package, may be partially manufactured prior to attachment to the article or package and then fully manufactured after attachment to the article or package, or the manufacturing process of the article or package may involve the manufacture of the RFID tag. In some embodiments, the RFID tag may be integrated into an article or package. In this case, the article or portion of the package may act as a label assembly. For example, the conductive article or packaging portion may act as a tag antenna segment or contact. The non-conductive article or packaging portion may act as a label substrate or inlay. If the article or package contains an integrated circuit or other circuitry, some portion of the circuitry may be configured to operate as part or all of the RFID tag IC. Thus, an "RFID IC" need not be different from an article, but more generally means an article that contains an RFID IC and an antenna capable of interacting with RF waves and receiving and responding to RFID signals. Because the boundaries between ICs, tags and articles are thus often ambiguous, the terms "RFID IC", "RFID tag", "tag" or "tag IC" as used herein may mean an IC, tag or even an article, provided that the referenced element is capable of RFID functionality.

The components of the RFID system of fig. 1 may communicate with each other in any number of modes. One such mode is known as full duplex, where both the reader 110 and the tag 120 may transmit at the same time. In some embodiments, RFID system 100 may be capable of full duplex communication. Another such mode that may be more suitable for passive tags is referred to as half-duplex and is described below.

Fig. 3 is a conceptual diagram 300 illustrating half-duplex communications between components of the RFID system of fig. 1, in which case tag 120 is implemented as a passive tag. The explanation is made with reference to the time axis, and also with reference to the human metaphors of "speaking" and "listening". Actual technical implementations for "speaking" and "listening" will now be described.

In half duplex communication mode, RFID reader 110 and RFID tag 120 speak to and listen to each other by rotating. As seen on the time axis, reader 110 speaks into tag 120 during the interval labeled "r→t" and tag 120 speaks into reader 110 during the interval labeled "t→r". For example, the sample R→T interval occurs during time interval 312 during which reader 110 speaks (block 332) and tag 120 listens (block 342). The subsequent sample t→r interval occurs during time interval 326 during which the reader 110 listens (block 336) and the tag 120 speaks (block 346). Interval 312 may have a different duration than interval 326, which is shown approximately equal for illustrative purposes only.

During interval 312, reader 110 transmits a signal, such as signal 112 depicted in fig. 1 (block 352), while tag 120 receives a reader signal (block 362), processes the reader signal to extract data, and collects power from the reader signal. While receiving the reader signal, the tag 120 does not backscatter (block 372), and thus the reader 110 does not receive a signal from the tag 120 (block 382).

During interval 326, also referred to as a backscatter time interval or backscatter interval, reader 110 does not transmit a signal carrying data. Conversely, reader 110 transmits a Continuous Wave (CW) signal, which is a carrier that does not substantially encode information. The CW signal provides energy for acquisition by the tag 120 and the tag 120 may be modulated to form a waveform of the backscatter response signal. Thus, during interval 326, tag 120 does not receive the signal with encoded information (block 366) and instead modulates the CW signal (block 376) to produce a backscatter signal, such as signal 126 depicted in fig. 2. Tag 120 may modulate the CW signal by adjusting its antenna reflectivity to produce a backscatter signal, as described above. The reader 110 then receives and processes the backscatter signal (block 386).

Fig. 4 is a block diagram showing details of an RFID IC, such as IC 224 in fig. 2. The circuit 424 may be implemented in an IC, such as the IC 224. The circuit 424 implements at least two IC contacts 432 and 433 that are adapted to couple to antenna segments such as antenna segments 226/228 in fig. 2. When two IC contacts form a signal input from an antenna and a signal returned to the antenna, they are often referred to as antenna ports. IC contacts 432 and 433 may be made in any suitable manner, such as from conductive pads, bumps, or the like. In some embodiments, the circuit 424 implements more than two IC contacts, particularly when configured with multiple antenna ports and/or coupled to multiple antennas.

The circuit 424 includes a signal routing section 435 that may include signal wiring, signal routing buses, receive/transmit switches, and the like, that may route signals between components of the circuit 424. IC contacts 432/433 may be galvanically, capacitively, and/or inductively coupled to signal routing section 435. For example, optional capacitors 436 and/or 438 may capacitively couple IC contacts 432/433 to signal routing section 435, thereby galvanically decoupling IC contacts 432/433 from signal routing section 435 and other components of circuit 424.

Capacitive coupling (and resultant galvanic decoupling) between IC contacts 432 and/or 433 and components of circuit 424 may be desirable in some circumstances. For example, in some RFID tag embodiments, IC contacts 432 and 433 may be galvanically connected to terminals of a tuning loop on the tag. In these embodiments, galvanically decoupling IC contact 432 from IC contact 433 may prevent a DC short from forming between the IC contacts through the tuning loop.

The capacitors 436/438 may be implemented within the circuit 424 and/or partially or entirely external to the circuit 424. For example, a dielectric or insulating layer on the surface of the IC containing circuitry 424 may serve as the dielectric in capacitor 436 and/or capacitor 438. As another example, a dielectric or insulating layer on the surface of the label substrate (e.g., inlay 222 or strap substrate 254) may serve as the dielectric in capacitors 436/438. The metal or conductive layers positioned on both sides of the dielectric layer (i.e., between the dielectric layer and the IC and between the dielectric layer and the tag substrate) may then act as terminals for the capacitors 436/438. The conductive layer may include an IC contact (e.g., IC contact 432/433), an antenna segment (e.g., antenna segment 226/228), or any other suitable conductive layer.

The circuit 424 includes a rectifier and Power Management Unit (PMU) 441 that harvests energy from RF signals incident on the antenna segments 226/228 to power the circuitry of the IC 424 during either or both of the reader-to-tag (r→t) and tag-to-reader (t→r) intervals. The rectifier and PMU 441 may be implemented in any manner known in the art and may include one or more components configured to convert Alternating Current (AC) or time-varying signals to Direct Current (DC) or substantially time-invariant signals.

Circuitry 424 also includes demodulator 442, processing block 444, memory 450, and modulator 446. Demodulator 442 demodulates RF signals received via IC contacts 432/433 and may be implemented in any suitable manner, such as using limiters, amplifiers, and other similar components. Processing block 444 receives output from demodulator 442, performs operations such as command decoding, memory interfacing, and other related operations, and may generate output signals for transmission. Processing block 444 may be implemented in any suitable manner, such as by a combination of one or more of a processor, memory, decoder, encoder, and other similar components. The memory 450 stores data 452 and may be implemented, at least in part, as a permanent or semi-permanent memory, such as a non-volatile memory (NVM), EEPROM, ROM, or other memory type configured to retain the data 452 even when the circuit 424 is not powered. Processing block 444 may be configured to read data from and/or write data to memory 450.

Modulator 446 generates a modulated signal from the output signal generated by processing block 444. In one embodiment, modulator 446 generates a modulated signal by driving a load presented by an antenna segment coupled to IC contacts 432/433 to form a backscatter signal as described above. In another embodiment, modulator 446 includes and/or uses a transmitter to generate and transmit a modulated signal via antenna segments coupled to IC contacts 432/433. The modulator 446 may be implemented in any suitable manner, such as using switches, drivers, amplifiers, and other similar components. Demodulator 442 and modulator 446 may be separate components, combined in a single transceiver circuit, and/or be part of processing block 444.

In some embodiments, particularly those with more than one antenna port, the circuit 424 may contain multiple demodulators, rectifiers, PMUs, modulators, processing blocks, and/or memory.

Fig. 5A shows a version 524-a of the components of the circuit 424 of fig. 4, further modified to emphasize signal operation during the r→t interval (e.g., time interval 312 of fig. 3). During the R→T interval, demodulator 442 demodulates the RF signal received from IC contacts 432/433. The demodulated signal is provided to processing block 444 as c_in, which IN some embodiments may include the received symbol stream. The rectifier and PMU 441 may be active, for example, harvesting power from an incident RF waveform and providing power to a demodulator 442, processing block 444, and other circuit components. During the r→t interval, the modulator 446 does not actively modulate the signal and may in fact be decoupled from the RF signal. For example, the signal routing section 435 may be configured to decouple the modulator 446 from the RF signal, or may adjust the impedance of the modulator 446 to decouple it from the RF signal.

Fig. 5B shows a version 524-B of the components of the circuit 424 of fig. 4, further modified to emphasize signal operation during the t→r interval (e.g., time interval 326 of fig. 3). During the t→r interval, processing block 444 outputs a signal C OUT, which may contain a symbol stream for transmission. Modulator 446 then generates a modulated signal from C OUT and sends the modulated signal via the antenna segments coupled to IC contacts 432/433 as described above. During the T→R interval, the rectifier and PMU 441 may be active, while the demodulator 442 may not actively demodulate the signal. In some embodiments, demodulator 442 may be decoupled from the RF signal during the t→r interval. For example, the signal routing section 435 may be configured to decouple the demodulator 442 from the RF signal, or may adjust the impedance of the demodulator 442 to decouple it from the RF signal.

In the exemplary embodiment, demodulator 442 and modulator 446 are operable to demodulate and modulate signals according to protocols such as the Gen2 protocol mentioned above. In embodiments in which circuitry 424 includes multiple demodulators, modulators, and/or processing blocks, each may be configured to support a different protocol or set of different protocols. The protocol specifies, in part, symbol encoding and may include a set of modulations, rates, timings, or any other parameters associated with data communications. The protocol may be a variant of an internationally formally validated protocol, such as the Gen2 protocol, for example, containing fewer or additional commands than are required by the formally validated protocol, and so on. In some examples, the additional commands may sometimes be referred to as custom commands.

Fig. 6 depicts an RFID reader system 600 according to an embodiment. The reader system 600 is configured to communicate with RFID tags and optionally with entities external to the reader system 600, such as the service 632. The reader system 600 includes at least one reader module 602 configured to transmit signals to and receive signals from RFID tags. The reader system 600 further includes at least one local controller 612, and in some embodiments, at least one remote controller 622. The controllers 612 and/or 622 are configured to control operation of the reader module 602, process data received from RFID tags communicating through the reader module 602, communicate with external entities such as the service 632, and otherwise control operation of the reader system 600.

In some embodiments, the reader system 600 may include a plurality of reader modules, a local controller, and/or a remote controller. For example, the reader system 600 may include at least one other reader module 610, at least one other local controller 620, and/or at least one other remote controller 630. A single reader module may communicate with multiple local and/or remote controllers, a single local controller may communicate with multiple reader modules and/or remote controllers, and a single remote controller may communicate with multiple reader modules and/or local controllers. Similarly, reader system 600 may be configured to communicate with a plurality of external entities, such as other reader systems (not depicted) and a plurality of services (e.g., services 632 and 640).

The reader module 602 includes a modulator/encoder block 604, a demodulator/decoder block 606, and an interface block 608. Modulator/encoder block 604 may encode and modulate data for transmission to the RFID tag. Demodulator/decoder block 606 may demodulate and decode the signal received from the RFID tag to recover the data transmitted from the tag. Modulation, encoding, demodulation, and decoding may be performed according to protocols or specifications, such as the Gen2 protocol. The reader module 602 may use the interface block 608 to communicate with the local controller 612 and/or the remote controller 622, such as exchanging tag data, receiving instructions or commands, or exchanging other related information.

The reader module 602 and blocks 604/606 are coupled to one or more antennas and/or antenna drivers (not depicted) for transmitting and receiving RF signals. In some embodiments, the reader module 602 is coupled to multiple antennas and/or antenna drivers. In these embodiments, the reader module 602 may transmit and/or receive RF signals on different antennas in any suitable scheme. For example, the reader module 602 may switch between different antennas to transmit and receive RF signals, transmit on one antenna but receive on another antenna, or transmit and/or receive on multiple antennas simultaneously. In some embodiments, the reader module 602 may be coupled to one or more phased array or composite beam antennas, the beams of which may be generated and/or steered, for example, by the reader module 602, the local controller 612, and/or the remote controller 622.

The modulator/encoder block 604 and/or the demodulator/decoder block 606 may be configured to perform conversion between analog signals and digital signals. For example, the modulator/encoder block 604 may convert digital signals received via the interface block 608 to analog signals for subsequent transmission, and the demodulator/decoder block 606 may convert received analog signals to digital signals for transmission via the interface block 608.

The local controller 612 includes a processor block 614, a memory 616, and an interface 618. The remote controller 622 includes a processor block 624, a memory 626, and an interface 628. The local controller 612 differs from the remote controller 622 in that the local controller 612 is collocated with or at least physically proximate to the reader module 602, while the remote controller 622 is not physically proximate to the reader module 602.

The processor blocks 614 and/or 624 may be configured to provide different functions, alone or in combination. Such functions may include: control of other components such as memory, interface blocks, reader modules, and the like; communication with other components such as the reader module 602, other reader systems, services 632/640, and the like; data processing or algorithmic processing such as encryption, decryption, authentication, and the like; or any other suitable function. In some embodiments, the processor blocks 614/624 may be configured to convert analog signals to digital signals or vice versa, as described above with respect to blocks 604/606; the processor blocks 614/624 may also be configured to perform any suitable analog signal processing or digital signal processing, such as filtering, carrier cancellation, noise determination, and the like.

The processor blocks 614/624 may be configured to provide functionality through execution of instructions or applications that may be retrieved from a memory (e.g., memory 616 and/or 626) or received from some other entity. The processor blocks 614/624 may be implemented in any suitable manner. For example, the processor blocks 614/624 may be implemented using: digital and/or analog processors, such as microprocessors and Digital Signal Processors (DSPs); a controller, such as a microcontroller; software running on a machine such as a general purpose computer; programmable circuitry, such as a Field Programmable Gate Array (FPGA), a Field Programmable Analog Array (FPAA), a Programmable Logic Device (PLD), an Application Specific Integrated Circuit (ASIC), any combination of one or more of these; and equivalents.

The memory 616/626 is configured to store information and may be implemented in any suitable manner, such as the memory types described above, any combination thereof, or any other known memory or information storage technology. The memory 616/626 may be implemented as part of its associated processor block (e.g., processor block 614/624) or separately. The memory 616/626 may store instructions, programs, or applications for execution by the processor blocks 614/624. The memory 616/626 may also store other data, such as files, media, component configurations or settings, and the like.

In some embodiments, memory 616/626 stores tag data. The tag data may be data read from the tag, data to be written to the tag, and/or data associated with the tag or tagged item. The tag data may contain an identifier for the tag, such as an Electronic Product Code (EPC), tag Identifier (TID), or any other information suitable for identifying the individual tag. The tag data may also contain a tag password, a tag profile, a tag encryption key (secret or public), a tag key generation algorithm, and any other suitable information about the tag or item associated with the tag.

The memory 616/626 may also store information regarding how the reader system 600 is to operate. For example, the memory 616/626 may store information regarding: algorithms for encoding commands for tags, algorithms for decoding signals from tags, communication and antenna modes of operation, encryption/authentication algorithms, tag location and tracking algorithms, encryption keys and key pairs (e.g., public/private key pairs) associated with reader system 600 and/or other entities, electronic signatures, and the like.

The interface blocks 608, 618, and 628 are configured to communicate with each other and with other suitably configured interfaces. Communication between the interface blocks occurs via the exchange of signals containing data, instructions, commands, or any other suitable information. For example, interface block 608 may receive data to be written to a tag, information regarding the operation of reader module 602 and its constituent components, and the like; and may transmit data read from the tag. Interface blocks 618 and 628 may send and receive tag data, information regarding the operation of other components, other information for enabling local controller 612 and remote controller 622 to operate in conjunction, and the like. The interface blocks 608/618/628 may also communicate with external entities, such as services 632, 640, other services, and/or other reader systems.

The interface blocks 608/618/628 may communicate using any suitable wired or wireless means. For example, the interface blocks 608/618/628 may communicate via circuit traces or interconnects, or other physical wires or cables, and/or using any suitable wireless signal propagation technique. In some embodiments, interface blocks 608/618/628 may communicate via an electronic communication network, such as a Local Area Network (LAN), metropolitan Area Network (MAN), wide Area Network (WAN), a network such as the Internet, or the like. The communication from the interface blocks 608/618/628 may be secure, e.g., via encryption and other electronic components, or may be unsecure.

The reader system 600 may be implemented in any suitable manner. One or more of the components in reader system 600 may be implemented as an integrated circuit using CMOS technology, BJT technology, MESFET technology, and/or any other suitable physical implementation technology. Components may also be implemented as software executing on general-purpose or special-purpose hardware.

In one embodiment, a "reader" as used in this disclosure may include at least one reader module similar to reader module 602 and at least one local controller, such as local controller 612. Such a reader may or may not include any remote controller, such as remote controller 622. The reader including the reader module and the local controller may be implemented as a stand-alone device or as a component in another device. In some embodiments, the reader may be implemented as a mobile device, such as a handheld reader, or as a component in a mobile device, such as a laptop computer, tablet computer, smartphone, wearable device, or any other suitable mobile device.

If not included in the reader, the remote controller 622 may be implemented separately. For example, remote controller 622 may be implemented as a local host, remote server, or database coupled to one or more readers via one or more communication networks. In some embodiments, remote controller 622 may be implemented as an application executing on the cloud or at a data center.

The functionality within reader system 600 may be distributed in any suitable manner. For example, the encoding and/or decoding functionality of blocks 604 and 606 may be performed by processor blocks 614 and/or 624. In some embodiments, processor blocks 614 and 624 may cooperate to execute applications or perform some functionality. One of the local controller 612 and the remote controller 622 may not implement memory, while the other controller provides memory.

The reader system 600 may be in communication with at least one service 632. Service 632 provides one or more features, functions, and/or capabilities associated with one or more entities, such as reader systems, tags, tagged items, and the like. Such features, functions, and/or capabilities may include: providing information associated with the entity, such as warranty information, repair/replacement information, upgrade/update information, and the like; and services associated with the entity such as storage and/or access of entity-related data, location tracking of the entity, entity security services (e.g., authentication of the entity), entity privacy services (e.g., who is allowed access to what information about the entity), and the like. The service 632 may be separate from the reader system 600 and both may communicate via one or more networks.

In some embodiments, the RFID reader or reader system implements the functions and features described above, at least in part, in the form of firmware, software, or a combination (e.g., hardware or device drivers, operating systems, applications, and the like). In some embodiments, interfaces to various firmware and/or software components may be provided. Such interfaces may include Application Programming Interfaces (APIs), libraries, user interfaces (graphical and other), or any other suitable interface. The firmware, software, and/or interfaces may be implemented via one or more processor blocks, such as processor blocks 614/624. In some embodiments, at least some of the reader or reader system functions and features may be provided as a service, for example, via service 632 or service 640.

RFID systems are often used to track RFID tagged items. RFID systems can track items with tags by determining the location of the tag, whether the tag is moving or stationary, and whether the tag is moving at its speed (i.e., its rate and direction of movement). Given (1) the distance from the RFID reader antenna to the tag (referred to as the "range") and (2) the direction from the RFID reader antenna to the tag, the RFID system can determine the location of the tag. The RFID system may further determine the tag speed based on the location of the tag as a function of time.

The RFID system may determine the range and/or motion of the RFID tag based on the propagation characteristics of the signal transmitted by the reader and/or the reply signal backscattered by the tag using the signal transmitted by the reader. For example, an RFID system may cause an RFID reader to transmit a signal having a known frequency and phase. The RFID tag will generate a tag reply signal by backscattering the signal transmitted by the reader. The backscattered tag reply signal will have a different phase relative to the signal transmitted by the reader, and the RFID system may use these different phases and the known frequency and phase of the signal transmitted by the reader to estimate one or more parameters of the RFID tag, such as its distance from the RFID reader, whether it is moving, and if so, the direction and/or rate of movement. In this disclosure, "phase" or "phase measurement" of a tag reply means the difference between the measured phase of the tag reply and the phase of the original reader transmit signal upon which the tag reply was backscattered.

Fig. 7 depicts tag parameter determination using phase according to an embodiment. RFID reader system 702 is configured to communicate with RFID tag 706 using one or more antennas 704, 724, and 744. At a first time, tag 706 is in position 710 such that tag antenna 708 is disposed at distance 712 from antenna 704, at distance 732 from antenna 724, and at distance 746 from antenna 744. In the present disclosure, the distance or range between two antennas is measured from the phase center of each antenna. The reader system 702 may first transmit a first signal 714 having a first frequency and then transmit a signal 718 having a second frequency. While the reader system 702 is transmitting the first signal 714, the tag 706 back-scatters a reply signal 716 on the first signal 714, the reply signal having the same first frequency as the first signal 714 but having a first phase relative to the first signal 714, wherein the first phase depends at least on the distance 712. Similarly, while the reader system 702 is transmitting the second signal 718, the tag 706 back scatters a reply signal 720 on the second signal 718, the reply signal having the same second frequency as the second signal 718 but having a second phase relative to the second signal 718, wherein the second phase depends at least on the distance 712. The reader system 702 may then estimate the distance 712 using the following equation:

Where R is the label range, c is the speed of light,is the difference between the first phase and the second phase (in reply signals 716 and 720, respectively), and Δf is the difference between the first frequency and the second frequency (of first signal 714 and second signal 718, respectively).

With only antenna 704, reader system 702 can estimate distance 712, thereby positioning tag 706 and antenna 708 on a spherical shell centered on antenna 704. If additional antennas are used by reader system 702, the locations of tag 706 and antenna 708 may be further refined. For example, reader system 702 may transmit signals 734 and 738 from antenna 724, each having a different frequency, and may receive reply signals 736 and 740 from tag 706, back-scattered on signals 734 and 738, respectively. Reply signal 736 will have a phase relative to signal 734 and reply signal 740 will have a phase relative to signal 740, wherein the phase depends at least on distance 732. The reader system 702 may then estimate the distance 732 using the equation above and position the tag 706 and antenna 708 onto a spherical housing centered on the antenna 724. If the relative and absolute positions of antennas 704 and 724 are known, tag 706 and antenna 708 may then be positioned on a circle formed by the combination of the two spherical shells centered on antennas 704 and 724. If the signal on the third antenna, such as antenna 744, is subsequently used to determine phase, tag 706 and antenna 708 may be further located depending on the position of the third antenna relative to the other two antennas.

In addition to tag location, reader system 702 may also be able to estimate other tag parameters such as motion or speed. Referring again to fig. 7, assume that tag 706 has moved from position 710 to position 750. At location 750, tag antenna 708 is now disposed at distance 752 from antenna 704, distance 772 from antenna 724, and distance 782 from antenna 744. While tag 706 is in position 750, reader system 702 transmits signal 754 and optional signal 758, having a third frequency and a fourth frequency, respectively. The tag 706 then back scatters a reply signal 756 on the signal 754, the reply signal having the same third frequency but a third phase relative to the signal 754 and dependent at least on the distance 752. If reader system 702 transmits optional signal 758, tag 706 can backscatter reply signal 760 on signal 758, with the same fourth frequency but with a fourth phase relative to signal 758 and dependent at least on distance 752. If the third frequency or the fourth frequency is the same or similar to the first frequency of the first signal 714 or the second frequency of the second signal 718, the reader system 702 may be able to directly compare the corresponding similar phases to determine that the tag 706 has moved or is in motion. Further, if the third frequency and the fourth frequency are different, the reader system 702 may use the third phase and the fourth phase to estimate the distance 752 as described above for the distance 712.

In some embodiments, reader system 702 may use additional antennas to enhance tag parameter determination at location 750. For example, reader system 702 may transmit signal 774 and optionally signal 778 from antenna 724, receive backscatter signals 776 and 780 on signals 774 and 778, respectively, from tag 706, and determine the phase of signals 776/780 relative to signals 774/778. Reader system 702 may compare the determined phases to each other (if signals 774 and 778 have different frequencies) or to the phases of signals 736/740 to estimate distance 772 and/or motion of tag 706. Reader system 702 may then refine the estimate of the position and/or motion of tag 706 using the distance/motion estimation performed on antenna 724 in combination with the distance/motion estimation performed on antenna 704. If other antennas (e.g., antenna 744) are available, the reader system 702 may perform phase measurements on those antennas to further refine the tag position/motion estimation.

The phase of the tag reply signal received by the reader system is not only dependent on the frequency of the signal and the distance between the reader system and the tag, but is also affected (added to or subtracted from) the reader system and/or the tag. This change to the phase by the reader or tag system may be referred to as an "additive phase". Characterization of the additive phase of the reader system or tag (also referred to as "calibration") may allow the RFID system to remove or compensate (in a process that may be referred to as "compensation") for effective changes in phase on the radio waves to more accurately determine (a) the propagation distance of the radio waves and (b) the tag location.

RFID reader systems typically include a transmitter, a receiver, one or more antennas, and an RF cable that connects the antennas to the transmitter/receiver. In many cases, the additive phase of the reader system is nonlinear with respect to frequency, and regardless of linearity, the RF cable and the reader device itself may contribute significantly to the additive phase.

The following description uses the terms additive phase and phase delay interchangeably to indicate the same phenomenon. In particular, the delay τ is equal to the derivative of the phase Φ of the radio wave with respect to the angular frequency ω:

fig. 8 depicts components of an RFID reader system 800 according to an embodiment. The RFID reader system 800 includes a reader transceiver 803 having an antenna port 802. Antenna port 802 is coupled to antenna 822 through RF cable 821. The reader transceiver 803 includes a transmitter 805, a receiver 806, and a frequency generator 804. The frequency generator 804 provides the operating frequency for the reader transceiver 803. The receiver 806 includes a demodulator 810 having a DC-coupled output 815 and an AC-coupled output 817.

The additive phase in the reader system 800 may come from delays in any of its components. In some embodiments, the delays of each component may be individually characterized, and the individual delays may then be combined (e.g., added or summed) to determine the total delay and additive phase of the reader system 800. In other embodiments, two or more components of reader system 800 may be combined, and the combined delays may be characterized. The additive phase phi of the reader system within the frequency range deltaf at the operating frequency f _rdr Total delay τ with reader system _rdr Correlation:

φ _rdr (f)＝τ _rdr (f)·2πΔf

in some embodiments, a Vector Network Analyzer (VNA) device may be used to measure delays of RF components such as RF cables and antennas. For example, the VNA may be used to measure the delay from a certain antenna using another reference antenna with a known delay and phase center.

The delay from the reader transceiver may be calibrated using static or dynamic reflection. Static calibration uses the DC output (e.g., output 815) of the IQ demodulator in the reader's receiver, while dynamic calibration uses the AC output (e.g., output 817) of the IQ demodulator.

Fig. 9 depicts how static reflection may be used to calibrate an RFID reader transceiver, such as reader transceiver 803, in accordance with an embodiment. In fig. 9, a load 901 having a non-zero reflection coefficient (e.g., an attenuator terminated by a short circuit) is placed at port 802 of a reader transceiver 803. The transceiver 803 is first energized to transmit at a frequencyFirst channel frequency f provided by generator 804 _c1 And (5) operating. While operating at the first channel frequency, the DC output 815 of the IQ demodulator 810 is measured to provide V _Idc1 And V _Qdc1 . Next, the frequency generator 804 is adjusted to provide a second channel frequency f _c2 . While operating at the second channel frequency, the DC output 815 of the IQ demodulator 810 is again measured to provide V _Idc2 And V _Qdc2 . If the two frequency channels are sufficiently close, f _c1 ≈f _c2 The reader transceiver delays τ _TxRx The method comprises the following steps:

wherein tan is ^-1 (. Cndot.) returns the arctangent in radians. This calibration assumes that the load 901 has no inherent delay. If the load 901 does have an inherent delay, then the inherent delay should be subtracted from the reader transceiver delay described above to characterize the true reader transceiver delay. For example, if the load 901 is a long RF cable terminated with a shorted attenuator, the inherent delay caused by the long RF cable should be subtracted to characterize the true and correct reader transceiver delay.

Fig. 10 depicts how dynamic reflection may be used to calibrate an RFID reader transceiver, such as reader transceiver 803, in accordance with an embodiment. In fig. 10, a load 1001 is coupled to a port 802 of a reader transceiver 803. In some embodiments, the load 1001 is configured to have an impedance value Z, respectively _R And Z _B Is switched between two known complex impedances 1002 and 1003. In these embodiments, switching between impedances occurs over time through electronic switch 1004 driven by modulation signal 1005b (t). If the source impedance looking into port 802 is Z _s Dynamic reflection will result in a dynamic complex reflection coefficient ΔΓ:

wherein the method comprises the steps ofRepresenting Z _S Is a complex conjugate of (a) and (b).

During dynamic reflection calibration, the DC output 815 of IQ demodulator 810 changes over time and is therefore unavailable for determining delay. Conversely, the difference between the voltage changes on the I and Q outputs measured at the AC output 817 of the IQ demodulator 810 may be used.

In one embodiment, transceiver 803 is first energized to provide a first channel frequency f at frequency generator 804 _c1 And (5) operating. At the first channel frequency, load 1001 may cause a voltage difference at AC output 817, which is measured as V _Iac1 And V _Qac1 . The transceiver 803 may then be energized to provide a second channel frequency f at a frequency generator 804 _c2 And (5) operating. While transceiver 803 is operating at the second frequency channel, another pair of voltage differences V at AC output 817 are measured _Iac2 And V _Qac2 . The reader transceiver delay may then be calculated based on the two pairs of voltage differences:

where arg {.cndot } returns the phase of the complex value in radians. The molecule arg of the second term ΔΓ (f) _c2 )}-arg{ΔΓ(f _c1 ) And } represents the phase delay caused by dynamic reflection. If the dynamics have no retardation, the phase arg { ΔΓ } of the complex reflection coefficient is constant in frequency, and if so, the equation for calibrating the transceiver retardation using dynamic reflection with an 'AC' voltage difference reduces to an equation for using static reflection with an absolute 'DC' voltage.

Reader system delay τ _rdr Is a combination of components of the system; transceiver τ including, but not limited to, a reader _TxRx、 RF cable τ _cbl And antenna tau _ant ：

τ _rdr (f)＝τ _TxRx (f)+τ _cbl (f)+v _ant (f)

As earlier describedStatic or dynamic calibration may be applied to the transceiver of the reader, but any calibration may be applied to a combination of components of the system. For example, attaching a dynamic reflection to a reader transceiver using the RF cable 821 of the reader system would measure the delay τ of the transceiver-cable combination _TxRx-cbl . If so, the total system delay will be:

τ _rdr (f)＝τ _TxRx-cbl (f)+τ _ant (f)

fig. 11 depicts how dynamic reflection in a radiating environment may be used to calibrate an RFID reader system, such as reader system 800, in accordance with an embodiment. In fig. 11, a reader system 800 communicates with a load 1001 coupled to a reference antenna 1106 having a known phase center, a known delay τ _ref (f) And a known impedance Z _S . If the phase center of antenna 822 is separated from the phase center of reference antenna 1106 by a distance d, then the reader system delay can be calculated as:

where c is the radio wave propagation rate (e.g., speed of light).

Once the reader system delay has been determined using any of the techniques described above or any other technique, the additive phase of the reader system _ar (f) Can then be determined as:

φ _ar (f)＝(2π·f·τ _rdr (f))modulo(2π)

where the (x) module (y) operator returns the remainder of x divided by y.

After the reader system has been calibrated, the additive phase φ _ar (f) Or phase delay τ _rdr (f) May be stored in an array or represented by a polynomial or by a linear equation. The backscatter phase measurements can be calibrated, modulated, after compensation in the reader or a host connected to the reader to provide compensated phase measurements. Compensated phase measurement phi _c Equal to the phase phi measured by the reader system _meas With the additive phase of the reader systemDifference between:

φ _c (f)＝φ _meas (f)-φ _ar (f)

as mentioned above, the RFID tag or tag system may also contribute an additive phase. For example, during a modulated backscatter process in which the tag sends information back to the reader, the tag may increase phase or phase delay. In this case, the compensated phase measurement φ _c Equal to the phase phi measured by the reader system _meas Subtracting the additive phase phi of the reader system _ar And the additive phase phi of the tag system _at ：

φ _c (f)＝φ _meas (f)-φ _ar (f)-φ _at (f)

The additive phase in backscatter modulation from the tag may result from a delay of the tag antenna, a change in impedance of the tag antenna, or a change in impedance in the integrated circuit of the tag. Furthermore, the additive phase may be indirectly from different operating frequencies, from different power levels incident on the tag, or from different materials in the vicinity of the tag.

Once the reader system additive phase and/or the tag system additive phase are known, the method for compensation of the phase measurements may be performed, for example, by the reader system or a host connected to the reader system.

A compensation method relates to the phase versus frequency phi of the tag additive _at Measurement and creation of a table (or equation) of dependencies of the same, and subsequent storage of the table or equation in a reader system or connected host. During operation, the reader system or host uses one or more of the frequencies and the table (or equation) to perform phase measurement compensation. The table (or equation) for compensation may be predetermined or the table may be dynamically selected based on information from the tag, e.g., the identifier. Other information that may be used to create the table (or equation) or perform phase compensation may include the type of material near the tag or the incident power level incident on the tag.

Another compensation method involves the RFID tag providing information about the tag phase delay, either directly or indirectly. The tag may provide information directly by sending tag-additive phase data or values known to or stored on the tag. The tag may indirectly provide information by sending data associated with its operation or backscatter, such as its current impedance value or impedance setting, the radiation incident power level detected at the tag, or any other suitable parameter. The tag may also indirectly provide information via some characteristic of its backscatter reply, such as its incident power level at the receiving reader. This incident power level may be denoted as a Received Signal Strength Indicator (RSSI). The RSSI of the tag reply is phase-correlated with the tag additive and varies with frequency. Thus, the reader can measure the RSSI of replies from tags at different frequencies and use the RSSI to estimate the tag additive phase. After receiving the information, the reader system or a connected host can use the information for phase compensation.

These two methods of compensating for the tag additive phase may be combined. For example, a table (or equation) of tag additive phases may include a dependence on frequency, incident power level at the tag, and/or tag impedance, and the reader system or connected host may determine tag additive phases based on the table (or equation), incident power information communicated from the tag, and/or tag impedance information communicated from the tag.

One problem associated with tag range determination based on phase measurements is that the periodic nature of the phase means that a certain phase value may correspond to multiple ranges. This limitation is sometimes referred to as the "n pi-mode problem". Some range determination techniques based on phase measurements address this problem by limiting the system environment or parameters to ensure that any phase difference does not exceed a maximum value. In contrast, the present disclosure solves this problem by using a process that does not require such limitations. In particular, rather than determining range or motion directly from phase measurements, multiple potential tag candidates are generated that each have a different range and/or motion. A candidate phase set is calculated for each candidate using known data, such as the frequency of the signal transmitted by the reader and the value of the reader system and tag system additive phase. The actual phase measurement of the real tag is then compared and correlated with the candidate phase. If the actual phase measurement is highly correlated with the calculated candidate phase for a certain candidate, the range/motion of that candidate is determined to match the range/motion of the real tag.

Fig. 12 depicts how RFID tag parameters, such as range or motion, may be determined by correlation with candidates according to an embodiment. Fig. 12 shows an RFID system 1201 comprising at least one tag 1202 and a reader system 1203. The reader system 1203 includes at least one antenna 1204 through which communication with the tag 1202 occurs. The antenna 1204 is further coupled to a reader transceiver 1205.

Using the reader transceiver 1205, the reader system 1203 may communicate with the tag 1202 to perform n+1 phase measurements at n+1 different frequencies (step 1250) to obtain several phase measurement/frequency pairs (Φ) of the tag 1202 _n ，f _n ). The phase measurement may be an unadjusted phase measured by the reader system 1203, or may be a compensated (as described above) phase value to account for, for example, an additive reader phase or tag phase.

To estimate the tag location, the reader system 1203 or connected host may generate a list of M tag candidates at step 1252. The tag candidates or "virtual tags" represent potential locations of an actual tag, such as tag 1202, and are preferably each located at a different distance from antenna 1204. At a distance d _m The candidate at will produce in its response back-scattered to the reader system 1203 a frequency and distance d that depend on the back-scattered (or carrier) signal _m Is a phase of (a) of (b). The n+1 different frequencies used in step 1250 may be used to calculate n+1 phases for each candidate in step 1254, where at a given frequency _n The phase ψ calculated for a given candidate m _mn Dependent on candidate distance d _m ：

Wherein n=0..n

In the calculation, to calculateAny constant phase offset between the phase measurements of the actual tags of the phase difference may be determined by arbitrarily determining the phase measurement phi for the actual tags ₀ Selected to pass through the reference frequency f ₀ The generated reference phases are removed to calculate N phase differences DeltaPhi _n ：

Δφ _n ＝φ _n -φ ₀ Wherein n=1..n

In a similar manner, the phase difference Δψ of the mth candidate can be calculated using the same reference frequency _mn ：

Δψ _mn ＝ψ _mn -ψ _m0 Wherein n=1..n and

in the above, the reference frequency f for phase difference ₀ May be arbitrary and the reference frequency is not limited to the lowest or highest frequency used in the phase measurement. In some embodiments, the quality of the phase measurements (described in more detail below) may be used to select a reference frequency f for determining the phase difference ₀ 。

Candidates with a distance consistent with the actual tag location will have a high correlation. In step 1256, the reader system 1203 or host computer calculates the correlation of the M tag candidates, wherein the correlation of the mth candidate is normalized by the number of measured phase differences N to determine the probability p of the mth candidate _m ：

After several phase measurements, has a high correlation probabilityMay appear singly as a viable candidate, and this viable candidate will have a distance d that is close to the distance of the actual tag (e.g., tag 1202) from the antenna (e.g., antenna 1204) _m . If all candidates have a low correlation probability p _m M=1.m, the low probability indicates no viable candidates and a low confidence in the distance that the actual tag was found.

Fig. 13 depicts a diagram of how correlation may be used to determine RFID tag range according to an embodiment. Diagrams 1310, 1320, and 1330 are graphs of relevant probability curves for three different phase measurement scenarios. The vertical axis of the graph represents the correlation probability, and the horizontal axis represents the number of tag candidates ordered according to their distance from the reader system antenna. For example, a tag candidate closer to the antenna will be to the left of a tag candidate further from the antenna.

Drawing 1310 depicts a correlation probability curve having a normalized value close to oneIs defined by a single defined peak of (a). This indicates that one viable candidate has been identified, and thus the associated distance of the one candidate from the antenna may be approximately equal to the distance from the antenna of the actual tag.

Drawing 1320 depicts a correlation probability curve having a low correlation probability with a normalized value significantly below one, indicating no viable candidates. Similarly, the diagram 1330 depicts a correlation probability curve with a number of significant correlation probabilities, also indicating no viable candidates.

In some embodiments, a candidate may be considered viable if (a) corresponds to a significant peak in the relevant probability and (b) is the only such significant peak. For example, a peak corresponding to a peak-only candidate in the correlation probability curve may be considered viable if its height exceeds a normalized value of about 0.5, otherwise not. If the correlation probability curve contains multiple significant peaks, all having similar heights (e.g., similar in diagram 1330), no peak may correspond to a viable candidate. On the other hand, if the correlation probability curve contains a plurality of significant peaks, one of which is significantly higher than the other peaks, candidates corresponding to the peaks may be considered viable. In some embodiments, the significance of the peak may be measured based on the noise floor of the correlation probability. For example, diagram 1310 depicts a noise floor having a normalized value of approximately 0.2-0.25. If the peak exceeds more than twice the noise floor, the peak may be considered significant, which in diagram 1310 will be a peak with a normalized value height of approximately 0.4-0.5.

The description has focused on one actual tag, but the method may be generalized for two or more actual tags, as the reader associates phase measurements with individual tags; in particular, the reader provides the identity of the tag and its phase measurement at a particular frequency.

In some embodiments, this method may also be generalized for two or more antennas on a reader system. For example, given a reader system of K antennas, each antenna has N _k A plurality of measured phase differences, phi, measured by the phase from each antenna _nk The phase difference delta phi of the kth antenna can be easily determined _nk ：

Δφ _nk ＝φ _nk -φ _0k Wherein n=1..n _k And k=1K

Similarly, the distance d between the mth candidate (virtual tag) and the kth antenna _mk Will determine the phase difference Δψ _mnk ：

Δψ _mnk ＝ψ _mnk -ψ _m0k Wherein n=1..n _k And k=1..k and

for candidates in two or three dimensions, the distance between the candidate (virtual tag) and the different antennas will often be different, e.g. d _mk ≠d _m(k+1) . Some candidates may be symmetrically located between antennas, e.g. d _mk ＝d _m(k+1) . The mth candidate uses K antennas to represent the probability p of the position of the actual tag _m The method comprises the following steps:

wherein the total number N of phase differences measured _tot Equal to the sum of the phase differences measured on all antennas:

For a reader system with a single antenna, each candidate represents a surface in three-dimensional space, and if the phase center of the antenna is fixed, the surface of the candidate is of radius d from the phase center _m Is a sphere of (2). For a reader system with first and second (two) antennas, the candidates represent curves resulting from the intersection of the two surfaces. If the phase centers of the two antennas are fixed, one sphere has a radius d to the first phase center _m1 And the other sphere has a radius d to the second phase center _m2 And the intersection point of the spheres is an arc. Finally, for reader systems with three or more antennas, the candidates represent points in space resulting from the intersection of multiple sphere surfaces.

Without limitation to the maximum phase difference, the frequency f _n Is infinite and in frequency hopping or frequency agile RFID systems the difference between the channel frequency and the channel frequency is similarly infinite. In addition, this process eliminates the need to avoid the "n pi mode problem" when placing the reader antennas, and thus the separation distance between two or more antennas is also not limited. Finally, this process does not require limiting the tag location to avoid the "n pi-mode problem" and thus the tag can be in any arbitrary location.

In some embodiments, the "quality" or "effectiveness" of the modulated backscatter measurement of the actual tag can be determined and used to enhance the process of determining the tag location. In these embodiments, each modulated backscatter phase measurement can be assigned a factor q _nk To indicate the quality or effectiveness of the nth phase measurement using the kth antenna. For example, the factor may be a binary value based on a threshold value, q in case the backscatter power is above the threshold value _nk =1, or in the opposite directionQ in case of a backscatter power below a threshold value _nk =0. In another example, the factor may be proportional to the modulated backscatter power. The factor may also be based on data information from the actual tag. For example, an actual tag may relay data whose operating power is low via modulated backscatter, and if so, the quality of the modulated backscatter is similarly low, e.g., q _nk ＝0。

In some embodiments, another factor Q may be defined _nk To represent the phase difference delta phi _nk Quality or effectiveness of (a). Quality factor Q for phase difference _nk May be defined independently or, for example, as the product of the quality factors of the phase measurements:

Q _nk ＝q _nk ·q _0k wherein n=1..n

No matter the phase difference quality Q _nk How the sum Q of the phase difference qualities can be defined _tot ：

Thus, the normalized correlation using the quality factor for each candidate becomes:

as described above, the RFID reader system may use different antennas and different frequencies to produce tag phase measurements. If the tag or surrounding environment is in motion, the phase measurements will change over time and these changes can be used to estimate the tag motion. It is assumed that the reader system has a+1 antennas in a single station configuration, and the tag phase measurement is from the a-th antenna, where a=0. Further assume that the phase measurement for one antenna is using K _a +1 frequencies are collected and the phase measurements are passed through the frequency f for each antenna a _ak Grouping, wherein k=0..k _a . Finally, assume that at a certain time t _akn Collecting N at each frequency and at each antenna _ak +1 phase measurements, where n=0..n _ak . At frequency f _ak The a-th antenna is used to measure collectively all phase measurements phi from one tag _akn . At time instance t _akn Each phase measurement is performed at, and a first phase measurement value phi is assumed ₀₀₀ Time t of (2) ₀₀₀ Is the earliest time, t ₀₀₀ ≤t _akn 。

The additive phase from the reader or from the tag caused by different power levels or by different frequencies may sometimes detract from the phase measurement phi _akn . To minimize the effect of additive phase, the phase difference between phase measurements from the same frequency and the same antenna measured at different times can be taken:

Δφ _aknr ＝φ _akn -φ _akr where n+.r

Optionally phase measurement phi _akr One of the choices of reference defines the phase difference delta phi _aknr . Using the phase difference of the same phase measurement r=n does not help in insight, since the phase difference is zero ΔΦ _aknn =0. In addition, the phase differences using the same pair of phase measurements are redundant and do not contribute to insight, as they are opposite Δφ _aknr ＝-Δφ _akrn . The phase difference from two (unique) phase measurements provides insight and using "N2" the number of phase differences for each frequency on one antenna is:

for example from one antenna a and one frequency f _ak Is a function of the four phase measurements N _ak +1=4 yields six unique phase differences:

Δφ _ak10 ，Δφ _ak20 ，Δφ _ak30 ，Δφ _ak21 ，Δφ _ak31 ，Δφ _ak32

tag using spherical coordinate system based on phase center of a-th antennaThe propagation distance from the a-th antenna depends on the (scalar) radial distance r between the tag and the antenna and the phase center of the tag _a (f, t). The phase center of the tag and antenna depends on the frequency f of the RF wave, while the movement between the tag and antenna will depend on the time t. Non-overlapping antennas will have phase centers at different locations, so the radial distance between the tag and the antenna will often (but not necessarily) be different.

Consider a population of virtual tags, referred to herein as candidates. For a number of candidates of m+1 and m=0..m, propagation phase ψ between mth candidate and a-th antenna _ma (f, t) depends on time t, frequency f, and radial distance r between the mth candidate and the phase center between the a-th antenna _ma (t，f)：

Where c is the rate of RF wave propagation.

If the motion of the mth candidate coincides with the motion of the (actual) tag, the candidate phase ψ _ma (f, t) will be different from at time t _akn And different frequencies f _ak Phase measurements from tags _akn And consistent. Phase measurement phi _akn And the phase ψ from the candidates _ma (f, t) the comparison may require coordination between the phase measurement and a time reference between the candidate phases. For example, the radial distance r between the mth candidate and the a-th antenna _ma (f, t) may use a reference t to a time stamp for phase measurement _akn Different times refer to t. In addition, the radial distance may be only at discrete times τ _i Available at, and may be between two time stamps, e.g., t _akn ＜τ _i ＜t _ak(n+1) 。

Currently, it is assumed that the time references are coordinated and that the candidate phases share the same time stamp and frequency used in the phase measurement:

the candidate has a motion consistent with the tag when the candidate phase and the tag phase have a high correlation probability. Let us assume that we have a signal from one antenna a, using the kth frequency f _ak N of (2) _ak +1 phase measurements, then the mth candidate from one antenna and one frequency represents the normalized probability p of tag motion _mak The method comprises the following steps:

given the phase measurements of the tag from one antenna on all frequencies, the mth candidate has a combined normalized probability p of motion consistent with the tag _ma The method comprises the following steps:

finally, given the phase measurements of the tag on all frequencies on all antennas, the combined normalized probability of the mth candidate having motion consistent with the tag is:

one probability per candidate can be evaluated at a time, e.g. p as described above _m Or the probabilities may be evaluated individually at a more granular level, e.g. probability p at each antenna _ma 。

For example, assume that the phase measurements of the tag are from two antennas. Further assuming that the direct propagation path between the tag and the first antenna is blocked and depends mainly on multipath propagation, the normalized probability of (all) candidates of the first antenna will be low. Now assuming that the second antenna has a direct propagation path with the tag and that the multipath propagation is small, the normalized probability of one candidate from the second antenna will be high if that candidate represents the motion of the tag.

The probability of computing a candidate will depend on several conditions. For fixed frequency operation, all phase measurements on one antenna are performed at one frequency, k=0→k=0, and assuming the number of phase measurements is 100, n ₀₀ =100. In this example, the number of terms in the summation is the inverse of the normalization constant,in the frequency hopping mode, it is assumed that the phase measurement is approximately divided by approximately six frequencies, k+1=6, and each frequency has approximately 17 phase measurements, +.>During frequency hopping, the number of summation terms at each frequency is equal to the inverse of the normalization term for each frequency, N _0k (N _0k +1)/2=136, so the total number of summation terms is approximately six times the amount for each frequency, (k+1) ·n _0k ·(N _0k +1)/2. The number of summation terms for one candidate using either a fixed frequency (5000) or using frequency hopping (816) can be reduced to reduce computational requirements. For example, the phase measurements and their associated candidate phases may be initially downsampled to use every third phase measurement, N' _0k ＝N _0k And/3 to reduce the summation term by a factor of nine. Correlation with the downsampled phase measurements may provide a rough indicator of what candidates are possible, and then new correlations with all phase measurements may be applied to the possible candidates for a complete evaluation and higher accuracy.

The total number of summation items used to evaluate all candidates is equal to the number of candidates m+1 times the summation item per candidate. Similar strategies may be applied to the number of candidates to reduce computational requirements. To reduce computation, the number of candidates may be reduced by reducing the spatial density of the candidates (e.g., the number of candidates per unit volume) or reducing the physical region in which the candidates are located. Reducing the density of candidates provides a rough indicator of possible candidates after the first correlation. Another set of candidates that are smaller in pitch and near the possible candidates may then be created at a higher density based on the locations of the possible candidates, and the second correlation of the higher density candidates used to provide more accuracy with less computation.

If there is a priori or in situ knowledge of the linear motion between the antenna and the tag, a series of candidates may be constructed. Assume that a volume of labels is moving along a line at a constant rate, with candidates in the volume. Using a 3D cartesian coordinate system, the volume is assumed to be a cuboid (rectangular solid) travelling along the X-axis at a constant rate s. Without loss of generality, it is assumed that the origin of the coordinate system coincides with the center of the cuboid base when time is zero. Under these hypothetical conditions, the vector representing the position of the mth candidate is:

Wherein the x, y and z components of the mth candidate are x respectively _m ，y _m ，z _m . Using the same coordinate system, a vector of phase centers for a fixed and frequency independent a-th antenna can be defined:

wherein the x, y and z components of the phase center of the a-th antenna are Ax respectively _a ，Ay _a ，Az _a . By simplifying the phase center of the candidate independent of frequency, the radial distance between the antenna and the phase center of the candidate in the cuboid is:

wherein the operator returns vector (scalar) distance. Using cartesian coordinates, the radial distance is reduced to:

multiple candidates may have the same radial distance for one antenna at the same time. For example, assume two candidates m andand->Having the same x component->And resides with different y and z componentsAnd->In the YZ plane of (c). Two candidates in the same YZ plane have their y and z components separated from the antenna (Ay) in the YZ plane _a ，Az _a ) Will have the same radial distance if the phase centers of (a) have the same distance:

the (same) radial distance of these candidates cannot be solved by one antenna, but two or more antennas in place will remove this ambiguity. If two different antennas a andand->With different positions in the YZ plane, Or->Candidates in the YZ plane may be resolved.

Two mirror candidates m andand->May have identical y and z components, +.>And->But travel in the opposite direction +.>Wherein the initial x-component is symmetrically placed from the antenna, < >>The two image candidates will have the same radial distance for one antenna, since the magnitude of the x-component is equal:

two antennas in different YZ planesRadial candidates may be resolved. Furthermore, if the magnitude of the rate s has ambiguity, two antennas in different YZ planes will reduce the need for accurate knowledge of the rate. In general, by linear motion in 3D space, two or more antennas are desirably located at different positions along the axis of motion,and its position should also be different in a plane perpendicular to the axis of motion,/for example>Or (b)

The extent of the cuboid and the density of candidates may be as large or as small as desired, depending on computational resources and knowledge of the object (a priori or in situ). Generally, more knowledge of an object reduces computing resources. For example, assume that the object is a cassette traveling on a (linear) conveyor system along the x-axis at a fixed rate, and that the cassette has a depth D, a width W, and a height H, which are positioned to coincide with the x, y, and z directions, respectively. For convenience, it is assumed that the coordinate system is arranged such that the bed of the conveyor system coincides with the XY plane. With this arrangement, candidates residing in the cuboid are limited in the z-axis to a height from zero to the box, 0.ltoreq.z _m And is less than or equal to H. If the width of the cassette and the coordinate system are centered relative to the conveyor belt, the candidates residing in the cuboid are limited to half the width of the cassette, |y _m W/2 is less than or equal to. Finally, if the center of the cartridge is relative to the depth D at the initial time t=0 _c Is known, candidates in the cuboid are limited to half the depth from the center, |x _m -D _c The I is less than or equal to D/2. This collective knowledge of the boxes reduces candidates for evaluation in the cuboid to:

with more computing resources, candidates and cuboids for evaluation may be expanded, which may reduce the need for detailed object knowledge and/or restrictions on object location. For example, if the cassette is rotated arbitrarily, so its depth and width are randomly oriented with respect to the x-axis and y-axis, the cuboid of candidates should cover any rotation of the cassette:

if DW _max =max { D, W)And->

Wherein max { ·, } operator provides the maximum of the two values.

If the rate of the conveyor is unknown, the candidates may be at different rates s _m And (3) moving:

candidates from multiple cuboids may be evaluated, or the cuboid may be a large volume covering several boxes or even the whole length of a (straight) conveyor belt, with sufficient computational resources.

Some conveyor systems often slow down, stop, or resume their motion, and if sufficient computing resources for the candidate are not available in these contexts, additional in-situ knowledge of the motion may reduce the computing resources required by the candidate. For example, a sensor that monitors the rate or movement of the belt (referred to herein as a belt sensor) may limit candidates for evaluation. If the belt sensor provides a position b (·) on the belt as a function of time τ of the reference sensor, the radial distance of the candidate becomes:

this radial distance using the belt sensor assumes that the belt stretch is insignificant and that the cassette remains in a fixed position on the belt. In general, the belt sensor may have its own time reference for measurement and if so, the time reference of the belt sensor needs to be synchronized with the time of the phase measurement. Assuming an offset time τ _off Make the belt sensorAnd the time t of the first phase measurement from the first phase measurement ₀₀₀ Correlation, τ+τ _off ＝t ₀₀₀ . The belt sensor may provide (discontinuous) discrete values of belt position at different time instances. Assume that a belt sensor is provided at a time instance τ adjacent to _i And τ _i+1 Two discrete samples b (τ _i ) And b (τ) _i+1 ) And assuming that the two samples define a phase measurement t _akn ：

τ _i +τ _off ≤t _akn ≤τ _i+1 +τ _off

If the two samples of belt positions are sufficiently close with a nearly constant rate of motion, linear interpolation between belt positions will yield a representative radial distance:

this radial distance derived from the belt sensor can be used to determine the phase of the candidate for evaluation, which is shown here repeatedly for clarity:

evaluating candidates in 3D space for arbitrary (nonlinear) motion may be performed with a priori knowledge of the motion or in situ knowledge of the motion by actuators or sensors. For example, a lidar sensor or a dual camera sensor may provide vector information regarding the motion of an object over time,it can be decomposed into different vector components:

suppose that the candidate moves with the object and shares the same trajectory:

the radial distance between the (stationary) antenna and the candidate will be:

and the radial distance becomes:

some sensors provide information about object size and orientation, and if so, this information can be used to refine candidate locations. The object is assumed to translate in space over time and rotate about the z-axis, with a rotation Θ (τ) provided by the sensor. In this case, the candidate is defined by a radius ρ in the XY plane translating with the object motion _m And angle theta _m Better represents:

the radial distance between the antenna and the candidate then becomes:

this last example of creating candidates based on object translation and object rotation shows that the object has six degrees of freedom; three for position and three for orientation. One or more of the degrees of freedom of many (but not all) environments are limited and if so, the number of candidates and associated computational requirements may be reduced.

Examples are for stationary antennas as well as moving objects and tags. However, the correlation and evaluation of probabilities of different candidates can accommodate and move antennas and stationary tags. Knowledge of the object or antenna motion from the sensor or actuator provides information to generate candidates and determine the radial distance between the antenna and the candidates. The phase of the candidate may be evaluated for consistency with the phase measurement of the tag by the radial distance of the candidate, and if the candidate has a high correlation with the phase measurement, the candidate represents the tag motion or position.

To measure phase at different signal frequencies, an RFID system may transmit a signal (e.g., a chirp or wideband signal) having substantial power at multiple frequencies. When the tag replies with a backscattered signal, the backscattered signal will contain signal components at a plurality of frequencies. The RFID system may then use the phase of those signal components relative to the original transmitted signal to estimate tag parameters such as range and motion, as described above. RFID systems can also measure phase at different signal frequencies by inventorying tags multiple times at different carrier frequencies. For example, the RFID system may inventory the tag in a plurality of consecutive inventory runs, each run using a different carrier frequency, and then determine the phase of the tag in the plurality of inventory runs.

In some cases, spectrum usage rules that limit the frequency range and power of the transmitted signal reduce the number of different frequencies that can be used simultaneously in a single signal, thereby reducing the accuracy of phase comparison based ranging. Furthermore, the reader may not be able to inventory the same tag more than once, especially if the tag is moving or there are a large number of other tags.

One way to address these challenges may be for the reader to change the carrier frequency within a single inventory round. This fast frequency switching, if properly done, allows the phase to be measured at multiple signal frequencies without conflicting spectrum usage regulations or having to inventory tags more than once.

Carrier frequency switching introduces high frequency noise (sometimes referred to as frequency/spectrum adjacent channel interference or switching noise) into the carrier waveform and should therefore be reasonably timed to avoid degrading the RF environment and/or violating spectrum usage regulations.

In some embodiments, the reader transmitting the RF waveform may be configured to switch frequencies when the amplitude of the RF waveform is relatively low to ensure that noise generated by any switching also has a relatively low amplitude. The RF waveform may have a low amplitude at some time, regardless of how (or even if) it is modulated. For example, an RF waveform centered near zero amplitude will always have a low amplitude at or near the zero crossing where the RF waveform transitions between positive and negative amplitudes.

The amplitude modulated RF waveform may additionally have a low amplitude based on how the waveform is modulated. Fig. 14 depicts example baseband, modulated, and modulated waveforms at an RFID reader, and is similar to the waveforms in appendix H of the Gen2 protocol. Waveform 1410 is an example sequence of three data symbols 0, 1, and 0 as described in section 6.3.1.2.3 of the Gen2 protocol. The data symbols in waveform 1410 encode data in the form of time durations at a particular amplitude (e.g., amplitude "1") before transitioning to a different amplitude (e.g., amplitude "0"). Thus, each data symbol includes at least one relatively high amplitude portion and at least one relatively low amplitude portion. For example, the first data symbol depicted in waveform 1410 includes a low amplitude portion 1412. The example sequence in waveform 1410 may then be converted to a Double Sideband (DSB) or Single Sideband (SSB) Amplitude Shift Keying (ASK) modulated waveform 1420. In the modulated waveform 1420, the low amplitude portion 1412 of the waveform 1410 has been converted to a low amplitude portion 1422. The modulated waveform 1420 may then be used to amplitude modulate the RF carrier waveform to produce a modulated waveform 1430 that may be transmitted to an RFID tag. In particular, modulated waveform 1430 is formed by using modulated waveform 1420 to shape the RF envelope of the RF carrier waveform such that the RF envelope of the resulting modulated waveform 1430 is similar to modulated waveform 1420. In the modulated waveform 1430, the portion corresponding to the high amplitude portion of the modulated waveform 1420 may be relatively unmodulated and maintain a relatively high amplitude, similar to the amplitude of the unmodulated carrier waveform. In contrast, the portion of modulated waveform 1430 that corresponds to the low amplitude portion of modulated waveform 1420 may be significantly modulated to have a relatively low amplitude. For example, the portion 1432 of the modulated waveform 1430 corresponds to the low amplitude portion 1422 of the modulated waveform 1420 and thus has a relatively low amplitude.

The difference between the high and low amplitudes in the amplitude modulated RF waveform may be characterized by a "modulation depth" that is the ratio of (1) the difference between the amplitude of the unmodulated portion (corresponding to the high amplitude) and the amplitude of the modulated portion (corresponding to the low amplitude) and (2) the amplitude of the unmodulated portion. For example, a modulated waveform having a modulation depth of 50% includes a modulated portion having half the amplitude of an unmodulated portion. A modulated waveform having a modulation depth of 90% includes a modulated portion having one tenth of the amplitude of an unmodulated portion. Generally, the modulation depth tends to be between 30% and 100% (inclusive), although other suitable modulation depths may be used.

Whether or not the RF waveform transmitted by the reader has low amplitude due to zero crossing or modulation, the reader may choose to switch frequencies during these low amplitude portions without interrupting the waveform transmission. The reader can know when the low amplitude portion will occur and can time its frequency switch accordingly. For example, a reader may identify low amplitude portions within data or commands that it will transmit, and may perform frequency transitions while transmitting the data or commands.

In some embodiments, the reader may identify or predict when low amplitude portions or pulses will occur based on knowledge of the data to be transmitted, and perform frequency transitions during those portions or pulses. For example, a reader may identify a low amplitude portion or pulse within a command that it will transmit, and may perform a frequency transition while transmitting the command. In this case, the reader may ensure that the average power of the RF waveform containing the entire command is sufficient for the tag to receive the command or otherwise operate without powering down during the frequency transition. After transmitting the amplitude modulated RF waveform with the command, the reader may transmit an unmodulated RF waveform to provide power for the receiving tag to complete processing the command and transmit a tag response (if present) back-scattered modulated onto the unmodulated RF waveform. Performing frequency switching when the transmitted amplitude modulated RF waveform has a relatively low amplitude reduces the amplitude of any noise component due to the switching.

In some embodiments, the reader may switch frequencies during transmission of the Gen2 delimiter symbol. Fig. 15 depicts delimiter symbols according to the Gen2 protocol. Drawing 1500 depicts reader-to-tag preamble and frame synchronization as described and depicted in section 6.3.1.2.8 and fig. 6.4, respectively, of the Gen2 protocol. The preamble and frame sync each include delimiters 1510 and 1520, respectively, which have a relatively low amplitude for a duration of approximately 12.5 mus. In some embodiments, the reader may determine or predict when a delimiter is scheduled to transmit based on knowledge of any response to be transmitted, and perform a frequency transition during the delimiter. Of course, in other embodiments, the reader may switch frequencies during transmission of any low amplitude symbol or amplitude modulated waveform portion, so long as the symbol or portion duration is compatible with commands and signaling in an appropriate command signaling scheme (e.g., gen2 protocol).

The reader may not necessarily switch frequencies only at the low amplitude portion of the transmitted amplitude modulated RF waveform or at pulses in the RF waveform. Conversely, the reader may be able to identify and switch frequencies at other portions of the RF waveform or pulses in the RF waveform that are appropriate for the amplitude and duration of the frequency switch. In some embodiments, the reader may determine its frequency switching behavior such that the resulting spectral characteristics (waveform frequency distribution or characteristics) meet a threshold. For example, the reader may configure its frequency switching behavior such that the resulting spectral characteristics meet an emission mask, such as the emission masks depicted in fig. 6.6 and 6.7 of the Gen2 specification. The reader may instead configure its frequency switching so that the resulting spectral characteristics do not interfere with nearby RF systems. In this latter case, the reader or a controller associated with the reader may be configured to determine the appropriate spectral characteristics and to appropriately adjust the frequency switching behavior of the reader.

The reader system may default to fast frequency switching behavior or may perform fast frequency switching only in certain situations. In some embodiments, when the reader determines that it is to perform frequency hopping, the reader may determine whether any tags with which it has recently communicated will require power during frequency hopping. For example, the reader may determine that the tag is performing some lengthy or power-intensive operation, that the tag stores or maintains some state information that would be lost in the event of a power interruption, and/or that the tag is performing some other operation that cannot be reversibly interrupted. The reader may perform a fast frequency switch if the reader determines that one or more tags will require power during frequency hopping. On the other hand, if the reader determines that no tag will require power during frequency hopping, the reader may not perform fast frequency switching. In some embodiments, the reader may be configured to always perform fast frequency switching.

The RFID reader system may perform fast frequency switching in any suitable manner. For example, an RFID reader system may simultaneously generate multiple carrier frequencies for fast switching. Commonly assigned U.S. patent No. 10,679,019 issued 6/9 in 2020 and incorporated herein by reference in its entirety describes several ways in which an RFID reader system may simultaneously generate multiple carrier frequencies. In one embodiment, the RFID reader system may include a plurality of frequency synthesizers, each configured to generate a different frequency. If two or more of the synthesizers produce different frequencies simultaneously, the reader can switch its transmitted carrier frequency between the different frequencies without waiting for the oscillator to settle. In another embodiment, the RFID reader system may generate a wideband signal, recover the desired frequency components from the wideband signal using a comb filter, and then select an appropriate or desired carrier frequency from the recovered frequency components. In another example, an RFID reader system may sequentially generate different carrier frequencies for fast frequency switching using a Digital Frequency Synthesizer (DFS).

In general, more replies from tags result in more phase measurement opportunities, which may help refine tag parameter determinations. In some embodiments, techniques to elicit multiple replies from RFID tags within a single inventory round may be used in addition to the rapid frequency switching behavior described above. In these embodiments, the reader or reader system may be configured to measure the phase of multiple replies from a single tag within the same inventory round. The phase measurements from multiple replies to moving the RFID tag within a single inventory round bypass the n pi-mode problem, as long as the movement of the RFID tag is not fast enough to allow a single phase value to correspond to multiple ranges. In one embodiment, the reader system may cause the tag to reply with its identifier multiple times. According to the Gen2 protocol, when a reader sends an ACK command to a tag in an inventory round, the tag may backscatter a reply containing an Electronic Product Code (EPC). In some embodiments, the reader may send an ACK, receive a tag reply containing the EPC, then send another ACK and receive another tag reply containing the EPC. In this way, it is ensured that the reader receives at least two tag replies from which the reader can measure the phase. Further, because the tag replies contain the same data, phase measurements for the tag replies can be easier than in the case where phase measurements are associated with tag replies having different contents. In these embodiments, the reader may switch the carrier frequency between transmitting the two ACKs so that the two phase measurements are at different frequencies, or may not switch the carrier frequency, particularly if the tag is moving relatively quickly. While the reader has been described above as using an ACK command to cause the tag to reply multiple times, any suitable command that causes the tag to reply multiple times (with or without the same data) within an inventory round may be used.

In other embodiments, the reader system may be configured to perform multiple phase measurements while receiving a single tag reply, particularly when the tag may be moving rapidly. Rapid tag movement may result in significant differences in measured phase within the same tag reply, even at the same frequency. The reader system may be configured to select the interval between successive phase measurements based on a preset timing or some knowledge of the tag. For example, if the reader system knows that a certain tag may be moving at a certain speed (e.g., based on sensor information as described above), the reader system may select an interval between successive phase measurements appropriate for that speed.

According to some examples, a method for an RFID system to estimate a location of an RFID tag may include: sequentially transmitting a first RF signal having a first frequency and a second RF signal having a second frequency within a single inventory round; receiving a first reply back-scatter modulated on a first RF signal and a second reply back-scatter modulated on a second RF signal from an RFID tag within the single inventory round; determining a first set of phase differences associated with the first answer and the second answer; attempting to correlate the first set of phase differences with at least a first plurality of candidates, wherein each candidate is associated with a respective location; and estimating a first location of the RFID tag based on the attempted correlation.

According to other examples, the first reply and the second reply may be in response to consecutive commands from the RFID reader. The continuous command may be an ACK command according to the Gen2 protocol. The first reply and the second reply may contain the same content. The first RF signal and the second RF signal may be transmitted by a single reader employing fast frequency switching. Determining the first set of phase differences may include: determining an initial set of phase differences; and removing at least one of the additive reader phase and the additive tag phase from the initial set of phase differences to produce a first set of phase differences.

According to a further example, attempting to correlate the first set of phase differences with at least the first plurality of candidates may include attempting to determine whether a single candidate has a significant correlation probability. Estimating the first location of the RFID tag may include estimating the location associated with the single candidate as the first location of the RFID tag if only the single candidate has a significant correlation probability, otherwise estimating the first location of the RFID tag is uncertain. The method may further comprise: sequentially transmitting a third RF signal having a third frequency and a fourth RF signal having a fourth frequency within another inventory round; receiving a third reply back-scatter modulated on a third RF signal and a fourth reply back-scatter modulated on a fourth RF signal from the RFID tag within the another inventory round; determining a second set of phase differences associated with the third answer and the fourth answer; attempting to correlate the second set of phase differences with at least a second plurality of candidates, wherein each candidate is associated with a respective location; estimating a second location of the RFID tag based on the attempted correlation of the second set of phase differences; and estimating movement of the RFID tag based at least on the first location and the second location. Receiving the first reply and the second reply may include receiving the first reply and the second reply at each of the first antenna and the second antenna; and the first set of phase differences may include a phase difference of the first and second replies with respect to the first antenna and a phase difference of the first and second replies with respect to the second antenna.

According to some examples, a method for an RFID system to estimate a speed of an RFID tag may include: transmitting a first set of consecutive RF signals within a first copy round, wherein each RF signal in the first set of RF signals has a different frequency; receiving a first set of replies from an RFID tag during a first memory round, wherein at least two replies in the first set of replies are backscatter modulated on two distinct RF signals in the first set of RF signals; transmitting a second set of consecutive RF signals within a second inventory round, wherein each RF signal in the second set of RF signals has a different frequency; receiving a second set of replies from the RFID tag during a second inventory round, wherein at least two replies in the second set of replies are backscatter modulated on two distinct RF signals in the second set of RF signals; determining a first set of phase differences associated with the first set of replies; determining a second set of phase differences associated with the second set of replies; attempting to correlate the first set of phase differences and the second set of phase differences with a plurality of candidates, wherein each candidate is associated with a respective speed; and estimating a speed of the RFID tag based on the attempted correlation.

According to other examples, the first set of replies and the second set of replies may be in response to successive commands from the RFID reader. The continuous command may be an ACK command according to the Gen2 protocol. The first and second sets of replies may contain the same content. The first set of RF signals and the second set of RF signals may be transmitted by a single reader employing fast frequency switching. Determining the first set of phase differences may include: determining a first initial set of phase differences; and removing at least one of the additive reader phase and the additive tag phase from the first initial set of phase differences to produce the first set of phase differences. Determining the second set of phase differences may comprise: determining a second initial set of phase differences; and removing at least one of the additive reader phase and the additive tag phase from the second initial set of phase differences to produce a second set of phase differences.

According to a further example, attempting to correlate the first set of phase differences and the second set of phase differences with the plurality of candidates may include attempting to determine whether a single candidate has a significant correlation probability. Estimating the speed of the RFID tag may include estimating the speed associated with the single candidate as the speed of the RFID tag if only the single candidate has a significant correlation probability, otherwise estimating the speed of the RFID tag to be uncertain. Receiving the first and second sets of replies may comprise receiving the first and second sets of replies at each of the first and second antennas. The first set of phase differences may include a phase difference of the first and second sets of replies with respect to the first antenna and a phase difference of the first and second sets of replies with respect to the second antenna.

According to some examples, a method for an RFID system to estimate a speed of an RFID tag may include: transmitting two identical commands within a single inventory round; receiving a first reply to one of the two commands and a second reply to the other of the two commands from the RFID tag within the single inventory round; determining a first set of phase differences associated with the first answer and the second answer; attempting to correlate the first set of phase differences with the first plurality of candidates; and estimating a speed of the RFID tag based on the attempted correlation.

According to other examples, a method for an RFID system to estimate a location of an RFID tag may include: sequentially transmitting a first modulated RF signal having a first frequency and a second modulated RF signal having a second frequency within a single inventory round, wherein transitions between transmitting the first modulated RF signal and transmitting the second modulated RF signal occur at low amplitude pulses in the first RF signal; receiving a first reply back-scatter modulated on a first modulated RF signal and a second reply back-scatter modulated on a second modulated RF signal from an RFID tag within the single inventory round; determining a first set of phase differences associated with the first answer and the second answer; and estimating a location of the RFID tag based on the first set of phase differences.

According to yet other examples, attempting to correlate the first set of phase differences may include performing correlation using at least one quality parameter. The quality parameter may comprise the quality of the backscatter measurement and the quality of the phase difference. The first plurality of candidates may include a first set of candidates associated with a first antenna and a second set of candidates associated with a second antenna. The first plurality of candidates may be generated based on data from a sensor, wherein the sensor may include at least one of a belt sensor, a lidar sensor, and a dual camera sensor. Attempting to correlate the first set of phase differences with at least the first plurality of candidates may include: attempting to correlate a first set of phase differences with the first plurality of candidates to determine a set of possible candidates; generating a second plurality of candidates based on the locations of the set of possible candidates, wherein each candidate of the second plurality of candidates is associated with a respective location and the second plurality of candidates has a higher spatial density than the first plurality of candidates; attempting to correlate a first set of phase differences with the second plurality of candidates; and estimating a first location of the RFID tag based on the attempted correlations with the second plurality of candidates.

As previously mentioned, embodiments are directed to using phase to determine RFID tag parameters. Embodiments additionally include a program and a method of operation of the program. A procedure is typically defined as a set of steps or operations leading to a desired result due to the nature of the steps and elements in a sequence. A program is typically advantageously implemented as a sequence of steps or operations for a processor, but may be implemented in other processing elements, such as an FPGA, DSP or other device as described above.

The execution of the steps, instructions, or operations of the program requires manipulation of physical quantities. Usually, though not necessarily, these quantities may be transferred, combined, compared, and otherwise manipulated or processed in accordance with steps or instructions, and they may be stored in a computer readable medium. These quantities include, for example, electrical, magnetic and electromagnetic charges or states of particles, matter, and in more general terms, any physical device or element. The information represented by the states of these quantities may be referred to as bits, data bits, samples, values, symbols, characters, terms, numbers, or the like. However, these and similar terms are to be associated with the appropriate physical quantities individually or in groups and are merely convenient labels applied to these appropriate physical quantities.

Embodiments further include a storage medium. Such media has stored thereon, either alone or in combination with other media, instructions, data, keys, signatures, and other data of programs made in accordance with embodiments. The storage medium according to the embodiment is a computer-readable medium, such as a memory, and is readable by a processor of the type mentioned above. If a memory, it may be implemented in any manner and using any of the techniques described above.

Even though the program may be stored in a computer readable medium, it need not be a single memory, or even a single machine. Various portions, modules, or features thereof may reside in a separate memory, or even in a separate machine. The individual machines may be connected directly, or through a network, such as a Local Access Network (LAN) or a global network such as the internet.

For convenience only, it is often desirable to implement and describe the program as software. The software may be singular or considered to be singular in terms of the various interconnected distinct software modules.

The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams and/or examples. To this extent, these block diagrams and/or examples contain one or more functions and/or aspects, and each function and/or aspect within these block diagrams or examples can be implemented individually and/or collectively by a wide range of hardware, software, firmware, or virtually any combination thereof. Some aspects of the embodiments disclosed herein may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and/or firmware would be well within the skill of one of skill in the art in light of this disclosure.

The present disclosure is not limited to the specific embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from the spirit and scope of the disclosure. Functionally equivalent methods and apparatus, in addition to those enumerated herein, are within the scope of the present disclosure, as will be apparent to those skilled in the art from the foregoing description. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that the present disclosure is not limited to particular methods, configurations, tags, RFICs, readers, systems, and the like, which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural depending upon the context and/or application. For clarity, various singular/plural permutations may be explicitly set forth herein.

Generally, terms used herein and particularly in the appended claims (e.g., bodies of the appended claims) are generally intended to be used as "open" terms (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "comprising" should be interpreted as "including but not limited to," etc.). If a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" (e.g., "a" and/or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number recited in an introduced claim recitation is explicitly recited, such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).

Further, in those instances where a convention analogous to "at least one of A, B and C, etc." is used, such a construction is generally intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B and C" would include but not be limited to systems having only a, only B, only C, A and B together, a and C together, B and C together, and/or A, B and C together, etc.). Any disjunctive words and/or phrases presenting two or more alternative terms, whether in the description, claims, or drawings should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "a or B" will be understood to include the possibility of "a" or "B" or "a and B".

For any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any recited range can be readily identified for a sufficient description and can be broken down into at least the same two, three, four, five, ten, etc. parts. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, a middle third, an upper third, and the like. All language such as "up to", "at least", "greater than", "less than", and the like, include the recited numbers and refer to ranges that can be subsequently broken down into sub-ranges as discussed above. Finally, a range includes each individual member. Thus, for example, a group having 1 to 3 units refers to a group having 1, 2, or 3 units. Similarly, a group of 1 to 5 units refers to a group of 1, 2, 3, 4, or 5 units, and so on.

Claims (10)

1. A method for an RFID system to estimate a location of an RFID tag, the method comprising:

sequentially transmitting a first RF signal having a first frequency and a second RF signal having a second frequency within a single inventory round;

receiving a first reply back-scatter modulated on the first RF signal and a second reply back-scatter modulated on the second RF signal from the RFID tag within the single inventory round;

determining a first set of phase differences associated with the first answer and the second answer;

attempting to correlate the first set of phase differences with at least a first plurality of candidates, wherein each candidate is associated with a respective location; and

a first location of the RFID tag is estimated based on the attempted correlation.

2. The method of claim 1, wherein the first reply and the second reply are in response to consecutive commands from an RFID reader.

3. The method of claim 2, wherein the continuous command is an ACK command according to the Gen2 protocol.

4. The method of claim 1, wherein the first reply and the second reply contain the same content.

5. The method of claim 1, wherein the first RF signal and the second RF signal are transmitted by a single reader employing fast frequency switching.

6. The method of claim 1, wherein determining the first set of phase differences comprises:

determining an initial set of phase differences; and

at least one of an additive reader phase and an additive tag phase is removed from the initial set of phase differences to produce the first set of phase differences.

7. The method according to claim 1, characterized in that:

attempting to correlate the first set of phase differences with at least the first plurality of candidates includes attempting to determine whether a single candidate has a significant correlation probability; and is also provided with

Estimating the first location of the RFID tag includes:

estimating the location associated with the single candidate as the first location of the RFID tag if only the single candidate has the significant correlated probability, otherwise estimating the first location of the RFID tag is uncertain.

8. The method as recited in claim 1, further comprising:

sequentially transmitting a third RF signal having a third frequency and a fourth RF signal having a fourth frequency within another inventory round;

Receiving a third reply back-scatter modulated on the third RF signal and a fourth reply back-scatter modulated on the fourth RF signal from the RFID tag within the other inventory round;

determining a second set of phase differences associated with the third answer and the fourth answer;

attempting to correlate the second set of phase differences with at least a second plurality of candidates, wherein each candidate is associated with a respective location;

estimating a second location of the RFID tag based on the attempted correlation of the second set of phase differences; and

the movement of the RFID tag is estimated based at least on the first location and the second location.

9. The method according to claim 1, characterized in that:

receiving the first reply and the second reply includes receiving the first reply and the second reply at each of a first antenna and a second antenna; and is also provided with

The first set of phase differences includes a phase difference of the first and second replies with respect to the first antenna and a phase difference of the first and second replies with respect to the second antenna.

10. A method for an RFID system to estimate the speed of an RFID tag, the method comprising:

Transmitting a first set of consecutive RF signals within a first copy round, wherein each RF signal in the first set of RF signals has a different frequency;

receiving a first set of replies from the RFID tag during the first memory round, wherein at least two replies in the first set of replies are backscatter modulated on two distinct RF signals in the first set of RF signals;

transmitting a second set of consecutive RF signals within a second inventory round, wherein each RF signal in the second set of RF signals has a different frequency;

receiving a second set of replies from the RFID tag during the second inventory round, wherein at least two replies in the second set of replies are backscatter modulated on two distinct RF signals in the second set of RF signals;

determining a first set of phase differences associated with the first set of replies;

determining a second set of phase differences associated with the second set of replies;

attempting to correlate the first set of phase differences and the second set of phase differences with a plurality of candidates, wherein each candidate is associated with a respective speed; and

the speed of the RFID tag is estimated based on the attempted correlation.